1. Field of the Invention
The present disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of fabricating the liquid crystal display device where fabrication process is simplified.
2. Discussion of the Related Art
Recently, a liquid crystal display (LCD) device has been in the spotlight because the LCD has high value added due to its low-power consumption and good portability.
An active matrix liquid crystal display (AM-LCD) device, which includes thin film transistors as a switching device for a plurality of pixels, has been widely used due to its high resolution and superiority in displaying moving images.
In general, the LCD device is fabricated through an array substrate process for forming a thin film transistor and a pixel electrode on an array substrate, a color filter substrate process for forming a color filter layer and a common electrode on a color filter substrate and a cell process for forming a liquid crystal layer between the array substrate and the color filter substrate.
FIG. 1 is a cross-sectional view showing a liquid crystal display device according to the related art. In FIG. 1, a liquid crystal display (LCD) device 35 according to the related art includes an array substrate 40, a color filter substrate 70 and a liquid crystal layer 90. The array substrate 40 and the color filter substrate 70 face and are spaced apart from each other, and the liquid crystal layer 90 is between the array substrate 40 and the color filter substrate 70.
A gate electrode 45 and a gate line 43 are formed on an inner surface of the array substrate 40, and a gate insulating layer 47 is formed on the gate electrode 45 and the gate line 43. A semiconductor layer 50 including an active layer 50a and an ohmic contact layer 50b is formed on the gate insulating layer 47 over the gate electrode 45, and source and drain electrodes 58 and 60 are formed on the semiconductor layer 50. The source and drain electrode 58 and 60 contact the ohmic contact layer 50b and are spaced apart from each other.
In addition, a passivation layer 63 is formed on the source and drain electrodes 58 and 60, and a pixel electrode 67 of a transparent conductive material is formed on the passivation layer 63. The passivation layer 63 has a drain contact hole 65 exposing the drain electrode 60 and the pixel electrode 67 is connected to the drain electrode 60 through the drain contact hole 65.
A black matrix 73 of a lattice shape having a plurality of openings is formed on an inner surface of the color filter substrate 70, and a color filter layer 76 including red, green and blue color filters 76a, 76b and 76c is formed on the black matrix 73. The red, green and blue color filters 76a, 76b and 76c are sequentially disposed in the plurality of openings. A common electrode 79 of a transparent conductive material is formed on the color filter layer 76. In addition, a plurality of column spacers 83 are formed on the common electrode 79. The plurality of column spacers 63 are spaced apart from one another and contact the common electrode 79 and the passivation layer 63.
Although not shown, an orientation layer for an initial alignment of liquid crystal molecules is formed on each of the pixel electrode 67 of the array substrate 40 and the common electrode 79 of the color filter substrate 70. A liquid crystal layer 90 is formed between the orientation layers of the array substrate 40 and the color filter substrate 70.
In the LCD device 35, the pixel electrode 67 is formed over the array substrate 40 and the common electrode 79 is formed over the color filter substrate 70 such that the liquid crystal molecules of the liquid crystal layer 90 are driven by a vertical electric field generate between the pixel electrode 79 and the common electrode 79.
Recently, an in-plane switching (IPS) mode LCD device, where the pixel electrode and the common electrode are formed over the array substrate and the black matrix, the color filter layer, the overcoat layer and the column spacer are formed over the color filter substrate, has been suggested. In the IPS mode LCD device, since the liquid crystal molecules of the liquid crystal layer are driven by a horizontal electric field between the pixel electrode and the common electrode, a property in a viewing angle is improved.
The color filter substrate for the LCD device according to the related art may be fabricated through a five-mask process. For example, the color filter substrate for the IPS mode LCD device may be fabricated through a five-mask process including: a step of forming the black matrix (a first mask process); steps of forming the red, green and blue color filters for the color filter layer (second to fourth mask processes); and a step of forming the column spacer (a fifth mask process) without a step of forming the common electrode.
The mask process may be defined by a photolithographic process and an etching process. For example, the mask process may include a plurality of unit steps such as a step of forming a photoresist layer having a photosensitivity on a material layer over a substrate, a step of irradiating a light onto the photoresist layer through a photomask having a transmissive area and a blocking area, a step of developing the irradiated photoresist layer to form a photoresist pattern, a step of etching the material layer using the photoresist pattern as an etching mask, and a step of stripping the photoresist pattern.
Accordingly, the mask process requires a plurality of apparatuses for the plurality of unit steps and a plurality of materials for the plurality of unit steps. In addition, it takes much time to perform the plurality of unit steps for the mask process. Since the mask process includes the plurality of unit steps, increase in number of the mask process causes increase in fabrication cost and fabrication time. For the purpose of reducing fabrication cost and improving productivity of the LCD device, it is required to reduce the number of the mask process.